Q37305: LONG Integer Parameter Passed to SUB Fails after Assignment

Article: Q37305
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00 buglist4.00b buglist4.50 B_BasicCom | mspl13_basic
Last Modified: 11-DEC-1989

A problem can occur in an .EXE program when you pass a LONG integer
parameter to a subprogram and then assign that parameter to a local
short integer. The long integer parameter becomes corrupted; the
program should have only changed the local short integer. This problem
does not occur inside the QuickBASIC QB.EXE environment.

Microsoft has confirmed this to be a problem in QuickBASIC Versions
4.00, 4.00b, and 4.50 and Microsoft BASIC Compiler Versions 6.00 and
6.00b (buglist6.00, buglist6.00b) for MS-DOS and MS OS/2. This problem
was corrected in Microsoft BASIC Compiler Version 7.00 (fixlist7.00).

This problem does not occur when the program is compiled with the
debug option (BC /D). To work around the problem, compile with the
debug option.

The following steps will demonstrate this problem:

1. Pass an integer to a subprogram whose formal parameter is declared
   to be a LONG integer.

2. Within the subprogram, initialize a temporary, short-integer
   variable, and assign the LONG integer parameter to it. This forces
   a type conversion from LONG to short integer.

3. Immediately print out the LONG integer parameter. Even though the
   program was not designed to change the LONG variable, it is
   corrupted (i.e., an unexpected value appears). The temporary,
   short-integer variable prints correctly.

The program code example below will work as expected inside the
QuickBASIC QB.EXE environment. However, when compiled into an
executable (.EXE file), the problem occurs. Note that all three PRINT
statements should return the same values (4).

The following is a code example:

DECLARE SUB foo (long1&, long2&)
CLS
CALL foo(4&, 4&)  ' Long or short integer constants both show problem.

SUB foo (long1&, long2&)
PRINT "initial parameters: ", long1&, long2&
temp1% = 0
temp2% = 0
temp1% = long1&   ' It is here where the type conversion takes place
temp2% = long2&   ' and long1& and long2& are corrupted.
PRINT "Parameters after assignment: "; long1&, long2&
PRINT "Temporary variables after assignment: "; temp1%, temp2%
END SUB

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.